1. Field of the Invention
This invention relates to a camshaft for an internal combustion engine and more particularly to a camshaft fabricated from separate component parts.
2. Description of the Prior Art
There has been increasing demand for lightweight internal combustion engines because of the energy savings they provide. In addition, there is also a demand for highspeed and high-capacity internal combustion engines. With this in mind, attempts have been made to provide camshafts which are not only lightweight but are also high in strength and abrasion resistance. Efforts have also been made to increase the productivity of methods for forming such camshafts.
Although forged camshafts have conventionally been used for carrying relatively low loads, those made of quench-hardened cast iron are generally used as the performance of an engine is increased.
However, a cast iron camshaft has technical disadvantages in that it is generally heavy, it may lose strength during use and may be deflected during use. In addition, defects can occur when a large camshaft is cast and, moreover, quenching techniques require special know-how for providing the chilled surface layer and controlled quench-hardening.
On the other hand, there are known camshafts with cam lobes made of a sintered alloy and a central stem formed of a steel tube having improved strength and decreased weight. In order to manufacture such cam shafts, however, the cam lobes and the stem are subjected to positioning both in the axial direction and the direction of rotation. The lobes are then coupled to the stem but, if defective coupling occurs at any one spot, the assembly will not be usable. Moreover, the manufacture of such a camshaft requires a complex indexing device for determining the position of the lobes in the direction of rotation, as well as in the axial direction. As a result, methods of forming such assemblies have extremely poor productivity.
Japanese Pat. No. 46-7644 discloses the use of a bulge process for manufacturing a camshaft having bearings in principal locations to reduce the weight of the camshaft. Nevertheless, that disclosure relates to only a small single unit camshaft and is not applicable to a large-sized camshaft.